1. Field of the Invention
The present invention relates generally to the field of portable electric humidifiers, and more particularly to an improved portable humidifier that is capable of selectively operating in an evaporative and/or warm mist mode.
2. Description of the Related Art
Portable humidifiers are commonly used to enhance environmental conditions in enclosed environments, which might include rooms in residential homes and commercial office buildings. These humidifiers have been found to be very effective in controlling the humidity in these environments during very dry weather and during winter months when low temperature outside air is used to heat the environment causing the relative humidity therein to be lowered to an uncomfortable level.
Various types of portable humidifiers have been used to increase the level of humidity in these environments and may be broken down into the following five broad categories: (1) evaporation type humidifier; (2) steam vaporization type humidifier; (3) warm mist type humidifier; (4) ultrasonic type humidifier; and (5) impeller type humidifier.
A number of well known evaporative humidifiers, such as those disclosed in U.S. Pat. Nos. 5,034,162, 5,143,655 and 5,143,656, employ a wick element or other porous medium which is partly submerged in cold water contained in a reservoir. Liquid flow is produced by capillary action from the reservoir to a non-immersed portion of the wick element disposed in the path of air flow generated by an electric blower. Air moving through the wick element evaporates the water content in the wick element and produces vapor (cool mist) which is dispersed into the surrounding environment to increase the humidification level therein.
Steam vaporization type humidifiers, such as that disclosed in U.S. Pat. No. 4,810,854, typically comprise a water reservoir and an electric heating element submerged in the water to vaporize the water into steam. In this type of device, steam at a temperature of at least 212.degree. F. is discharged directly into the environment to be humidified.
Warm mist type humidifiers have been effectively used to achieve very high humidification levels. Typical warm mist humidifiers are disclosed in U.S. Pat. Nos. 5,014,338, 5,067,169, 5,111,529, 5,131,070, 5,133,044 and 5,143,460, which employ an electric heater coil for converting water contained in a reservoir into steam vapor. The steam vapor rises through a vapor passage and is mixed with air drawn through the passage by an electric blower. The air-vapor mixture (also referred to as "warm mist") is thereafter discharged into the environment to increase the humidification level therein.
While steam vaporization and warm mist type humidifiers both heat the water reservoir to its boiling point, warm mist humidifiers discharge a warm mist (rather than steam) into the environment to be humidified. Because the water reservoir is initially heated to its boiling point, many medical practitioners highly recommend warm mist type humidifiers due to their ability to forestall the growth of micro-organisms in the water reservoir, which otherwise could be subsequently carried by the air stream into the environment and ingested by persons therein.
Ultrasonic type humidifiers, such as those disclosed in U.S. Pat. Nos. 4,752,422, 4,752,423 and 4,921,639, generally comprise a reservoir filled with cool water which is atomized by intense vibration generated by a high frequency ultrasonic transducer. The transducer typically comprises a nebulizer which vibrates quietly at greater than 1 1/2 million times per second in order to convert the water into a fine, cool mist. An air stream created by an electric blower is directed onto the water surface and carries the cool mist out of the humidifier into the environment to be humidified.
Impeller type humidifiers typically employ an upright siphoning tube having a lower end positioned within the water reservoir and an upper end positioned vertically above the water reservoir. The siphoning tube is rotated axially by an electric motor such that water entering an orifice in the lower end of the tube is drawn upwardly through the tube toward its upper end. The siphoned water is then discharged in the form of droplets from the upper end of the rotating tube through a plurality of openings located near the top of the tube. The discharged water is directed against an atomizing screen thereby breaking the discharged water droplets into smaller particles to form a mist. Air being drawn through the humidifier by a fan mixes with the mist and this humidified air is discharged from the humidifier into the surrounding environment.
Presently, there is a tremendous amount of confusion amongst consumers as to whether to purchase a humidifier which discharges a cool mist (such as an evaporative type or impeller type humidifier) or one which discharges a warm mist (such as a warm mist type humidifier). This confusion is accentuated by the fact that medical practitioners and consumers frequently prefer different humidification methods depending upon the reason requiring humidification and even based upon the time of year.
For instance, warm mist humidification is frequently recommended for treating respiratory conditions and/or seasonal afflictions such as rhinitis sicca (commonly referred to as dry nose and/or throat). This preference for warm mist humidification may be predicated, at least in part, upon the soothing effects of the warm mist produced by the warm mist humidifier and/or the ability of warm mist humidifiers to forestall the growth of micro-organisms in the water reservoir by initially bringing the water to a boiling point.
In contrast, however, evaporative type humidifiers producing a cool mist are frequently recommended for daily use in the fall and winter months. This preference for cool mist humidification may be predicated, in part, upon the fact that the cool mist produced by evaporative type humidifiers does not cause an increase in the temperature of the environment to be humidified. Moreover, evaporative type humidifiers may be more energy efficient to operate due to the absence of heating elements and may not increase the evaporation rate of moisture from human skin as a result of elevated room temperatures.
To add to the confusion regarding the benefits of warm mist versus cool mist humidification, several manufacturers have recently marketed evaporative type humidifiers that include an electric heating element for increasing the moisture output. These modified evaporative type humidifiers employ an electric heater to elevate the water temperature in the reservoir and/or an electric heater to elevate the temperature of the air being drawn into the humidifier. However, in contrast to true warm mist humidifiers, these modified evaporative type humidifiers only utilize wick filters and do not elevate the temperature of the water in the reservoir to a boiling point, thereby forestalling the growth of micro-organisms therein.